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Tan K.W.,Advanced Materials for Micro and Nano Systems | Tan K.W.,Massachusetts Institute of Technology | Koh Y.K.,DSO National Laboratories | Chiang Y.-M.,Advanced Materials for Micro and Nano Systems | And 3 more authors.

In the colloidal self-assembly of charged particles on surfaces with opposite polarity, disorder often dominates. In this report, we show that ionic strength, volume fraction, and solvent evaporation temperature can be optimized in the vertical deposition method to yield hexagonal close-packed monolayer arrays with positively charged colloids on negatively charged bare glass. We further extend our study to form well-defined binary two-dimensional superlattices with oppositely charged monolayers grown layer-by-layer. Our results suggest that the lack of particulate mobility in oppositely charged systems is the main cause of disorder, and maximum mobility is attained when all three growth parameters are finely adjusted to increase the time scale for the particles to stabilize and order during crystal growth in these attractive systems. A clear understanding and control of the collective behavior of highly mobile colloids could lead to the creation of greater diversity of nanoarchitectures. © 2010 American Chemical Society. Source

Zhang K.,Advanced Materials for Micro and Nano Systems | Zhang K.,Nanyang Technological University | Zhang Q.,Advanced Materials for Micro and Nano Systems | Zhang Q.,Nanyang Technological University
Journal of Physical Chemistry C

Intact or broken sidewall C-C bonds on covalently functionalized single-walled carbon nanotubes (SWCNTs) play a fundamental role in preserving the excellent quantum conductance and electronic structure of SWCNTs. However, there has been a lack of experimental identification on possible sidewall C-C broken bond caused by covalent functionalizations. In this work, clear evidence of sidewall C-C bonds broken by [2 + 1] cycloaddition are observed with Raman scatterings on individual SWCNTs with various diameters and chiralities. The relationship between SWCNT chirality and dichlorocarbene grafting configurations is also observed for the first time. © 2015 American Chemical Society. Source

Esterina R.,Advanced Materials for Micro and Nano Systems | Liu X.M.,National University of Singapore | Ross C.A.,Advanced Materials for Micro and Nano Systems | Ross C.A.,Massachusetts Institute of Technology | And 4 more authors.
Journal of Applied Physics

The dewetting behaviors of cobalt (Co), cobalt palladium (CoPd), and palladium (Pd) thin films on oxidized silicon substrates were examined. We observed the formation of craters in the oxide layer and pits in the Si substrate for larger CoPd or Pd catalyst particles and thinner oxide. Nanowires and nanotubes were observed near the Si pits. The nanowires and nanotubes grow via a vapor-solid-solid or vapor-liquid-solid mechanism with the silicon vapor source provided from the substrate. The original Si atoms that form the nanowires or nanotubes were oxidized in situ by the residual oxygen atoms present in the chamber. Some of the nanotubes had a series of embedded sub-catalysts that formed branches from the primary nanotube. © 2012 American Institute of Physics. Source

Susantyoko R.A.,Advanced Materials for Micro and Nano Systems | Susantyoko R.A.,Nanyang Technological University | Wang X.,Nanyang Technological University | Xiao Q.,Nanyang Technological University | And 4 more authors.

We fabricated nickel oxide (NiO) on vertically-aligned multiwall carbon nanotube (MWCNT) arrays (MWCNT/NiO) as an electrode for lithium-ion batteries. The specific capacity of 864.8 mA h g-1 at the rate of 143.6 mA g-1 for up to 50 cycles was achieved. Compared to the electrode based on NiO thin film on stainless steel, the MWCNT/NiO showed significant improvements because the vertically-aligned MWCNT arrays enabled easy ion and electron transport and acted as excellent base-structures that minimize pulverization of the active materials by absorbing the compressive and tensile stresses during charge and discharge processes. Electrochemical impedance spectroscopy of MWCNT/NiO showed low internal resistance and low charge-transfer resistance of the MWCNT/NiO that suggest superior ion and electron transport, respectively. This demonstrated that the vertically-aligned MWCNT array is a promising current collector for conversion-type active materials. © 2013 Elsevier Ltd. All rights reserved. Source

Yun J.,National University of Singapore | Wang R.,National University of Singapore | Choi W.K.,Advanced Materials for Micro and Nano Systems | Choi W.K.,National University of Singapore | And 7 more authors.

A cost-effective method was used to fabricate large area (e.g. 2.5 × 2.5 cm2 for a pitch of 0.5 μm) nanometer scale pyramid arrays with precise and controllable location, spacing and size by interference lithography. Using this method a large-area of vertically-aligned carbon nanofibers (VACNFs) with different interfiber-distance-to-fiber-height ratios and fiber aspect ratios were synthesised. Very sharp tipped VACNFs were obtained and their field emission properties were measured and are compared to results in the literature. We find that the field emission performance of VACNF arrays is optimized when the interfiber-distance-to-fiber-height ratio is equal to 1, in line with some experimental findings but different from some predictions. © 2009 Elsevier Ltd. All rights reserved. Source

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